Title

Author

Semester of Graduation

Fall 2017

Degree

Master of Science (MS)

Department

Renewable Natural Resources

Document Type

Thesis

Abstract

The quantity and quality of dissolved carbon delivered to coastal margins by rivers is an important component of global carbon cycling. The Atchafalaya River (AR) discharges ~25% of the flow of the Mississippi River (MR) and the total flow of the Red River (RR) into the Gulf of Mexico (GoM) annually while flowing through the largest bottomland swamp in North America. This provides a unique opportunity to study floodplain impacts on dissolved carbon processes in a large river system. The research aimed to: (1) determine DIC and DOC transport and processing by a river swamp basin under varied seasons and flow conditions, using the AR as a case study; (2) describe how the major tributaries of the AR affect dissolved carbon concentrations and dynamics (3) provide much-needed estimates for export of carbon to the GoM by the AR. From May 2015 -May 2016, I analyzed DOC and DIC concentrations, mass loads, and δ13Cstable isotope composition of waters in the AR’s tributaries, and its origin and outlet locations.

The RR contributed the majority of DOC to this system. The MR contributed the majority of DIC. During the study period, the AR exported 5.35 Tg DIC and 2.34 Tg DOC into the GoM. Based on the mass inflow-outflow balance, approximately 0.53 Tg (~10%) of the total DIC exported was produced within the floodplain, while 0.24 Tg (~10%) of DOC entering the basin was removed. All sites were saturated with pCO2, indicating that this swamp-river system acts a large source of DIC to the atmosphere as well as to coastal margins. Largest downstream changes to concentrations and loads occurred during periods when the adjacent wetlands were deeply inundated. The changes corresponded with shifts in isotopic composition that suggested inputs of DIC from floodplains. This effect was particularly pronounced during early flood stages. This thesis research demonstrates that a major river with extensive floodplains in its coastal margin can act as an important source of DIC and a sink for DOC.